A pan-coronavirus fusion inhibitor targeting the HR1 domain of human coronavirus spike

Xia, Shuai; Yan, Lei; Xu, Wei; Agrawal, Anurodh Shankar; Algaissi, Abdullah; Tseng, Chien-Te K.; Wang, Qian; Du, Lanying; Tan, Wenjie; Wilson, Ian A.; Jiang, Shibo; Yang, Bei; Lu, Lu

Safety is obviously very important for the development of EK1 in clinical applications, and therefore, we first tested its in vitro cytotoxicity on various target cells. EK1 is not cytotoxic at concentrations up to 1 mM, which is more than 200 times higher than its IC 50 for inhibiting any HCoV S-mediated cell-cell fusion and pseudovirus entry ( fig. S3C ). We then further investigated its cytotoxicity in vivo. We continuously administered mice with PBS, low-dose EK1 (20 mg/kg), or high-dose EK1 (100 mg/kg) by intranasal route every day for 1 week, and we recorded the body weight changes for the following 2 weeks ( fig. S3D ). The EK1-treated mice in both high-and low-dose groups lived normally, with no apparent difference in weight gain/loss observed as compared to PBS-treated mice. Meanwhile, we used enzymelinked immunosorbent assay (ELISA) to measure EK1-specific antibodies in sera of mice 2 weeks after intranasal administration. No EK1-specific antibodies were detected in either the EK1treated group or in the PBS-treated group ( fig. S3E ).